1. Field of the Invention
The present invention relates to a method for acquiring map information required for displaying, e.g. a road map of the vicinity of a present situation, a method of navigation and a method of providing area information as well as a navigation apparatus and an area information providing apparatus to which the above methods are applied, and a navigation apparatus.
2. Description of the Related Art
In the past, various navigating apparatus which are mounted on a mobil object such as a car or the like have been developed. This navigation apparatus comprises a data storage means of large capacity such as a CD-ROM or the like in which, e.g. a road map data are stored, a detector unit means for detecting a present position, and a display unit for displaying the road map of the vicinity of the detected present position on the basis of readout data from the data storage means. In this case, the detector unit means for detecting the present position includes a position measuring system using an artificial satellite for position measuring, which is termed GPS (Global Position measuring System--hereinafter merely referred to as GPS) and which is based on an autonomous navigation which detects the moving direction, the moving speed, etc. of a vehicle to track the changes from a starting point to the present position.
The road map data of the vicinity of the present position, which are detected by such means for detecting the present position, are read out of the data storage means of large capacity such as the CD-ROM or the like to produce a video signal for displaying the road map. This video signal is supplied to the display unit for displaying the road map of the vicinity of the present position.
By the way, the navigation apparatus as described above requires the data storage means of large capacity for storing the road map and the detecting means for detecting the present position accurately, both of which are to be mounted on each vehicle. This involves a problem in which the apparatus is made extremely large-scale. Specifically, the road map data storage means requires the detailed map data of an area where a car carrying this apparatus moves. Such data have an enormous amount of information and so need the data storage means of large capacity using a storage medium such as the optical disc or the like as well as a readout means of the storage medium. Moreover, as concerns the position measuring means, in case of the position measuring system, e.g. by the aforesaid GPS, it is necessary to receive signals from a plurality of artificial satellites and calculate the present position by operational processings that use the signals received from the respective satellites, which involves very complicated operational processings. This raises the problem that circuits for the operational processings become large-scale.
Furthermore, as regards the road map data storage means using the storage medium such as the optical disc or the like, unless its storage medium is exchanged, it is difficult to revise the road map data to new data. For this reason, a user who possesses the navigation apparatus needs to replace the storage medium storing the road map data with a new version thereof at some intervals (e.g. annually) so that a new opened road, etc. may be displayed on the map, which involves a problem that it takes much time and cost to renew the road map data.